The present invention generally relates to a method of ultrasonic flaw detection of long-distance pipelines such as, for example, trunk oil pipelines, oil-products pipelines, and gas pipelines. More specifically, acoustic communication between one or more ultrasonic transducers and the pipe walls (for example, by means of a fluid plug) is provided by passing inside the pipeline a so-called xe2x80x9cpig,xe2x80x9d or an inspection probe, which is put into the pipeline and is conveyed by the fluid flow in the pipeline. Typical inspection pigs have built-in transducers, measuring instruments, devices for conversion and recording of the measured data, and a device that acquires digital data during the pig travel and processes the obtained data to detect flaws in the pipe walls and to determine the parameters of the detected flaws, as well as their position in the pipeline.
Known in the art is a method of in-tube ultrasonic flaw detection (U.S. Pat. No. 4,162,635) carried into effect by passing inside a pipeline a inspection pig having ultrasonic transducers, means for measurement, processing and storage of the measurement data. The traveling pig emits ultrasonic probing pulses towards the walls and receives the respective reflected ultrasonic pulses.
Also known in the art is a method of in-tube ultrasonic flaw detection (U.S. Pat. Nos. 5,587,534, 4,964,059, 5,497,661, 5,062,300) using a thickness metering technique. In accordance with this technique, an inspection pig that accommodates ultrasonic transducers and means for measurement, processing and storage of the measured data is passed inside the pipeline. During the pig travel the pulse transit time is measured by emitting ultrasonic probing pulses and by receiving the ultrasonic pulses reflected from the internal and external walls of the pipeline.
In accordance with these known techniques, making measurements with accuracy sufficient for inspection, identification of flaws, and determination of their parameters requires use of high-capacity memory devices. However, the pig traveling inside a pipeline has a limited volume for arrangement of data storage devices.
Several data transfers accompany the use of standard devices for compressing the data stored in files, irrespective of the physical nature of these data. At a low amount of transfers the compression is ineffective. The use of archiving algorithms such as Zip, Arj, Rar, and other efficient compression routines is accompanied by plenty of transfers of the compressed data. In so doing the amount of transfers and, respectively, the archiving time depends on the type and character of the data and is not restricted from above. For this reason, the time of data processing can exceed the reserved time and lead to errors in subsequent processing of the data and, respectively, to loss of some data.
Also known in the art is a method of in-tube ultrasonic flaw detection (U.S. Pat. No. 5,460,046 using the thickness metering method. In accordance with this technique, a pig (flaw detector) is passed inside the pipeline, said pig carrying ultrasonic transducers and devices for measuring, processing and storing the measured data. The measured data are generated by emitting ultrasonic probing pulses during the pig travel, receiving the respective ultrasonic pulses reflected from the internal and external walls of the pipeline, and by measuring the pulse transit time.
This method is characterized in that the values corresponding to the pipeline wall thickness within permissible limits are neglected, and what is recorded are only the values corresponding to the wall thickness below a permissible value.
During the in-tube ultrasonic flaw detection of pipelines, which have pipes whose thickness is beyond the permissible limits for the pipeline being tested, the measured data of the part of the pipeline corresponding to such pipes are recorded in a full scope even if they have no flaws.
Known in the art is another method of in-tube ultrasonic flaw detection (U.S. Pat. No. 4,909,091) by passing an inspection pig inside a pipeline, said pig carrying ultrasonic transducers, devices for measuring, processing and storing the measured data by emitting ultrasonic probing pulses during the pig travel and receiving the respective ultrasonic pulses reflected from the internal and external walls of the pipeline, and measuring the pulse transit time.
This method is characterized in that the measured successive values, which are rejected within a predetermined range of values, are recorded as a function of a number of successive values.
When testing the pipelines having pipes of different types and with a different thickness of the wall (with a difference in the wall thickness exceeding the error of thickness measurement and, respectively, the preset range width) the data measured in the part of the pipeline corresponding to the rated wall thickness for the pipes of a given section are not within the predetermined range and are not compressed.
The most similar with claimed method is a known in the art (U.S. Pat. No. 5,635,645) method of in-tube ultrasonic flaw detection of pipelines by passing inside the pipeline an inspection pig (flaw detector) carrying ultrasonic transducers, means for measurements, processing and storing the measured data, by emitting ultrasonic probing pulses and receiving the reflected pulses corresponding to said probing pulses, by obtaining data on the time intervals corresponding to the transit time of said pulses, and by conversion and storage of the measured data in the process of passing inside the pipeline.
During the data conversion in this method a sequence of the obtained values of the pulse transit time is formed, the number of obtained values of said sequence within a certain range being calculated and recorded in a storage device.
This method is characterized in that the range of values is set by a nominal value and a window symmetric relative to the nominal value. The nominal value is determined for each sequence of the obtained values by averaging the sequence values.
The main disadvantage of the known method is that in the presence of elongated lamination of metal in the wall of the pipe being tested or other flaws, the average value, as a rule, is beyond the range corresponding to rated pipeline wall thickness and beyond the range corresponding to the metal lamination. As a result, neither the values corresponding to the rated wall thickness nor the values corresponding to the laminations are in the range near the average value and, therefore, are not compressed.
The claimed invention is a method of in-tube ultrasonic flaw detection of pipelines is effected by passing inside a pipeline an inspection pig carrying ultrasonic transducers, devices of measuring, processing and recording the measured data (devices for measurements, processing and measured data storage), by emitting ultrasonic probing pulses during the pig travel and receiving the reflected pulses corresponding to said probing pulses, by obtaining data on the time intervals corresponding to the transit time of said pulses, by converting and recording (conversion and storage of) the measured data; during said data conversion a sequence of the obtained values of the transit time of the ultrasonic pulses is formed, the number of obtained values of said sequence within a certain (definite) range being calculated and recorded in a storage device.
The present invention differs from the prior art in a number of material respects. For example, in the process of data conversion, an area of values of a certain width is found, which has the maximum number of obtained values of said sequence, said range of values is found, in which at least one value relates to the found area of values. The number of obtained values of said sequence within said range is recorded in the storage device together with a code uniquely corresponding to said area of values and/or said range of values.
One of advantages that is obtained as a result of effecting the claimed invention is, for example, a decrease of size of the storage devices used when scanning the pipeline of a given length or an increase of the pipeline distance inspected for one pig travel at a given amount of the stored data.
The mechanism for attaining said technical result is that, for example, when processing the measured data corresponding to the laminations in the wall of the pipe with extended corrosion damage, the data sequences corresponding to the joint of pipes with different wall thickness, according to an exemplary embodiment of the claimed method, a range is found corresponding to the most probable value in the sequence of values.
This range corresponds either to the nominal thickness of the pipe wall (of whatever thickness it might be) or to the wall lamination, or to nominal thickness of the wall of one of the pipes in the joint of pipes of different thickness, or to the most frequently repeating value of depth of corrosion of a large extent. In all said and similar cases, the most frequently repeating values (within the range) in the sequence are compressed.
The obtained values that do not fall in said range of values are recorded directly in the digital data storage device.
As a still further exemplary development of the claimed invention, an average value of the range of values is determined, the digital data storage device is used for recording the retrieved average value of the range of values and the number of obtained values following in succession in a sequence laying in said range of values.
In a general case, the required area of values and the range of values may not coincide. Thus, the range width defines the inspection pig resolution and the amount of compressed data. The width of the required area of values determines the time of execution of the area search algorithm.
Said range of values uniquely corresponds to said area of values according to a predetermined (preset) rule.
In one exemplary embodiment of the claimed method, said range of values coincides with the found area of values. Such an embodiment allows, for example, one to achieve the highest degree of compression with no restriction on the time of execution of the algorithm.
In still another embodiment of the method the width of said range of values is directly proportional to the width of the found area of values. Such an embodiment allows one to optimize the width of a required area of values to match inspection pig hardware capability on the data processing without changing the width of said range of values and, respectively, the inspection pig resolution.
In order to find the above-mentioned range of values, some part of the obtained values from said sequence is taken into account. It is preferable to retrieve said range of values from a certain interval of the obtained values of said sequence corresponding to the ultrasonic pulses reflected from the area of pipeline wall.
Such a restriction allows one to exclude from the analysis on determining the most probable obtained values the data carrying no physical information on the wall thickness, for example, data corresponding to the ultrasonic pulses, reflected from the internal wall of the pipeline and not reflected from the external wall, as well as the ultrasonic pulses reflected from the media interface beyond the pipeline external wall.
In one exemplary application, the width of above range of values makes 0.3-10% of the maximum permissible obtained value in said sequence. The execution of the method at a smaller width of the range results in an unjustified decrease of the resolution (below the sufficient resolution for flaw detection) and, therefore, an increase of the amount of compressed data. At a greater width of the range the resolution is increased respectively, especially when inspecting the trunk gas pipelines, and the detection of flaws in the wall is complicated.
The amount (quantity) of the obtained values in said sequence of values is within a range of 200-5000. A sequence of digital values of the transit time of said ultrasonic pulses is formed in the process of measurements, the digit capacity of said digital values being not less than 5. In the preferable embodiment, the digit capacity of said digital values is not less than 7. This allows one to obtain resolution of 0.2 mm at a wall thickness of up to 25 mm.
At a certain low number of the obtained values in a sequence, the efficiency of the method at the faultless sections of the pipeline with a constant wall thickness is reduced because the number of formed sequences and, respectively, the number of recordings in a storage device per pipeline unit length of the grows up.
At a higher number of the obtained values in a sequence corresponding to about 16 m along the pipeline length, the efficiency of the method on the pipeline sections with multiple flaws such as xe2x80x9claminationxe2x80x9d or the like, drops down because in the presence of several flaws of the xe2x80x9claminationxe2x80x9d type per one sequence at the lamination extent greater than the extent of the faultless section of the pipeline, those values are compressed that correspond only to one most extended lamination.
During the measurements the ultrasonic pulses are received that are reflected from the internal and external walls of the pipeline, and the pulse reflected from the pipeline internal wall triggers the counter to count the time interval between the moment of arrival of the pulse reflected from the internal wall and the moment of arrival of the pulse reflected from the external wall of the pipeline. The above time intervals are measured by the moments of exceeding the predetermined threshold by an electric signal from the ultrasonic transducer corresponding to the received ultrasonic pulse.